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DG Joint Research Centre. Formal and informal approaches to the quality of information in integrated assessment Stefano Tarantola January 24-25, 2002 Laxenburg, Austria. Tools for Extended quality assurance. Information used as input to policy-making is complex, uncertain and disputed.

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DG Joint Research Centre

Formal and informal approaches to the quality of information in integrated assessment

Stefano Tarantola

January 24-25, 2002 Laxenburg, Austria

http://www.jrc.cec.eu.int/uasa

tools for extended quality assurance
Tools for Extended quality assurance

Information used as input to policy-making is complex,

uncertain and disputed.

Established guidelines: egNUSAP and model Pedigree schemes for the quality assurance of the decision

process.

Silvio.funtowicz@jrc.it

http://www.jrc.cec.eu.int/uasa

to set the frame

Chair in Man. Bus. Econ., UCLA

Alternative frameworks

Models

Indicators

Space of the assumptions

Space of the inferences

To set the frame

[Leamer, 1990 ] (economist):

“I propose a form of organised sensitivity analysis in which a neighborhood of alternative assumptions is selected and the corresponding interval of inferences is identified.

http://www.jrc.cec.eu.int/uasa

to set the frame1

Alternative frameworks

Space of the assumptions

To set the frame

“Conclusions are judged to be sturdy only if the neighborhood of assumptions is wide enough to be credible and the corresponding interval of inferences is narrow enough to be useful.”

Edward E. Leamer, 1990 “Sensitivity Analysis would help”, in Modelling Economic Series, Edited by CWJ Granger, Clarendon Press, Oxford. Chair in Man. Bus. Econ., UCLA

http://www.jrc.cec.eu.int/uasa

to set the frame2

we apportion such variability to its constituents

(the input factors) in the space

of the assumptions (or input space).

Decomposition of

model prediction

uncertainty

To set the frame

We move one step further: after characterising the interval of inferences (using e.g. the statistical variance),

Input factors should be

interpreted in sensu lato:

- alternative assumptions,

- choice of model,

- algorithmic alternatives,

- poorly-known data...

http://www.jrc.cec.eu.int/uasa

the case study incineration vs landfill austria 1994

Y

The Case Study: incineration vs. landfill (Austria 1994)

Robustness

assessment fails:

the interval of the

inference

is too wide

No defensible choice is

possible given the uncertainties.

http://www.jrc.cec.eu.int/uasa

the case study incineration vs landfill austria 19941
The Case Study: incineration vs. landfill (Austria 1994)

A

B

Space of the assumptions

Output uncertainty

http://www.jrc.cec.eu.int/uasa

settings for the sensitivity analysis
Settings for the sensitivity analysis

To validate or invalidate assessments

GSA used to show that the uncertainty in the decision on

whether to burn or dispose solid waste depends on the choice

of the system of indicators, and not on the quality of the

available data.

Money should not be spent to improve quality in data, but

to reach a consensus on the proper system of indicators.

Tarantola et al., in Saltelli et al. Eds, (2000)Sensitivity Analysis John Wiley

V(Y)=V[E(Y|Xi)]+E[V(Y|Xi)]

http://www.jrc.cec.eu.int/uasa

settings for the sensitivity analysis1
Settings for the sensitivity analysis

Problem simplification and dialogue optimisation

We look for those uncertain factors that have negligible

influence on the output.

These can be fixed to the most plausible value within

their range of variation.

The dimensionality of the input space is then reduced.

Useless discussing about the use of different architectures to build the composite indicator, when these do not influence the result.

http://www.jrc.cec.eu.int/uasa

settings for the sensitivity analysis2
Settings for the sensitivity analysis

Output uncertainty reduction

Joint use of UA and GSA (iterative procedure).

Perform UA and get a confidence interval for the output

If it is unacceptably large, acquire better knowledge on the

most important factors. Perform UA again to check ...

It the output quality exceeds the requirements,

the specifications on the input quality can be relaxed,

starting from the less important factors.

Crosetto and Tarantola (2001) Int J Geogr Inf Science

http://www.jrc.cec.eu.int/uasa

bibliography
Bibliography

[1] Saltelli, A., K. Chan, M. Scott, Editors, 2000, Sensitivity analysis, John Wiley & Sons publishers, Probability and Statistics series.[2] Saltelli, A., Chan, K., Scott, M. Eds., 1999, Special Issue on sensitivity analysis, Computer Physics Communications, 117. [3] Saltelli A., Tarantola S., and Chan K., 1999, A quantitative, model independent method for global sensitivity analysis of model output, Technometrics, 41(1), 39-56. [4] Saltelli A., Tarantola S., Campolongo F., 2001, Sensitivity analysis as an ingredient of modelling, Statistical Science, 15(4), 377-395.

http://www.jrc.cec.eu.int/uasa